1. Field of the Invention
The present invention is in the field of laser multiplexing, and in particular relates to the coherent beam combination of the output of multiple phase-locked optical amplifiers or lasers to produce a high-power diffraction-limited laser source.
2. Description of the Related Art
The peak far-field intensity produced by M phase-locked optical amplifiers or lasers of equal power can ideally be M times as great as the intensity produced by the same sources if their relative phases are random. This fact has motivated a great deal of work on achieving coherently phased optical sources. An example is a device which phases the output of 19 phase-locked diode lasers by sending this light through single-mode optical fibers. [L. Bartelt-Berger, U. Brauch, A. Giesen, H. Huegel, and H. Opower, "Power-scaleable system of phase-locked single-mode diode lasers," Appl. Opt. 38, 5752-5760 (1999).] Piezoelectric transducers are used to stretch the fibers so as to shift the optical phases. The optimal phases are maintained by means of an electronic feedback circuit.
Phase control is only one aspect of the problem of coherent beam combination. Generally the far-field of a phased array of emitters has power distributed partially into side lobes, so that the central peak contains only a fraction of the total power. To some extent this problem can be reduced by the use of microlens arrays which collimate the light from the individual sources when it has diffractively spread almost to the point of overlapping. [J. R. Leger, M. L. Scott, and W. B. Veldkamp, "Coherent addition of AlGaAs lasers using microlenses and diffractive coupling," Appl. Phys. Lett. 52, 1771-1773 (1988).] This increases the filling factor of the array, which is the ratio of the sub-beam diameters at their waists to the distance between beams. A large filling factor results in a greater fraction of far-field power in the central lobe. However, the microlens array does not produce a Gaussian beam, and the beam quality is not diffraction limited.
It is an object of the present invention to produce a high-power polarized Gaussian beam that is diffraction limited by multiplexing narrow-bandwidth phase-locked beams from multiple lasers or laser amplifiers. It is a further object to demultiplex a common optically encoded signal, such as a cable television signal, into multiple optical pathways.